Paleobiota of the Chinle Formation
The Chinle Formation is an extensive geological unit in the southwestern United States, preserving a very diverse fauna of Late Triassic animals and plants. This is a list of fossilized organisms recovered from the formation.
Amniotes
Archosauromorphs
Ornithodirans
Prosauropod tracks are present in the Redonda, Sloan Canyon, and Sheep Pen Sandstone formations. Possibly the Rock Point Formation as well. Geographically, the tracks are present in New Mexico.Theropod tracks have been found in Utah and New Mexico recovered from the Redonda, Sloan Canyon, and Sheep Pen Sandstone formations. Indeterminate theropod remains are stratigraphically present in the Petrified Forest, Bluewater Creek, and Rock Point members of New Mexico.
Plants
The Chinle Formation has a diverse flora of plant megafossils, though they are concentrated in only a few sites with suitable conditions. One of the most diverse floral communities is found near Fort Wingate, New Mexico. Paleobotanists have traditionally placed the Fort Wingate plant beds into the Monitor Butte Member, though more recently they are placed within the Bluewater Creek Formation, a subunit of the Chinle Formation first defined in 1989. Some Fort Wingate plant fossils belong to the "Lake Ciniza beds", a localized patch of grey mudstone corresponding to an ancient lake.Another productive areas for plant fossils is Petrified Forest National Park in Arizona. Though petrified wood could be found through the entire stratigraphy of the park, most other plant fossils are exclusive to greenish mudstone layers adjacent to the Newspaper Rock sandstone bed in the Blue Mesa Member.
Conifers are the most common and diverse plants, including petrified wood and leafy branches from massive trees as well as smaller shrubby forms. Cycad and bennettitalean leaves and other remains make up a significant portion of the flora. Ferns are abundant, with a range of growth habits including low shrubs, tree ferns, and palm-like fronds comparable to their modern relatives. Sphenophytes have low diversity but high abundance, and the largest Neocalamites fossils in the Chinle Formation could reach up to 6 meters in height. "Seed ferns" ginkgophytes, and small lycopods were present but uncommon. The flora is rounded out by unusual low-growing gymnosperms such as Sanmiguelia, Dechellyia, and Dinophyton.
The floral composition of the Chinle Formation seem to shift with changes in climate over time. The lowest parts of the Chinle, such as the Shinarump Conglomerate, are dominated by the bennettitalean Eoginkgoites alongside the first occurrence of other persistent plants such as Phlebopteris, Equisetites, and most common conifer species. Subsequent subunits are much more diverse, with a wide array of humidity-adapted plants making up the typical Chinle flora. This second floral zone is characterized by Dinophyton, a common but enigmatic shrubby gymnosperm. Plant fossils are rare in the upper part of the Chinle Formation, which was presumably much drier than the lower part. In these later layers, by far the most common plant fossils belong to Sanmiguelia alongside conifers and horsetails.